Many modern groupware applications generally require that each of a number of participants have his or her own computer. There are many occasions, however, in which two or more people wish to collaborate in a single-computer situation. This may occur, for example, when one person visits another's office, or when two or more people are using a large-screen computer, such as a Xerox LIVEBOARD.RTM. interactive display system, which is described in Proceedings of CHI,92, ACM Conference on Human Factors in Computing Systems, May 3-7, 1992, Monterey, Calif., pgs. 599-607. for per-user customization. Those that do usually take advantage of the fact that each user has his or her own computer and is running a separate instance of an application. Prior systems have not permitted customization such that the same instance of the application and the same screen can be shared. The superscript identifications in the following discussion refer to the Bibliography at the end of this disclosure.
Shared window systems.sup.1 in the past have allowed users to share standard applications over a network. Some systems of this type are of the What You See Is What I See (WYSYWIS) type. Work on shared window systems has focused on sharing unmodified single-user applications, maintaining a networked conference, and floor control. These systems have experienced difficulties in maintaining consistent views between displays when local user preferences are honored.
Networked conference-aware systems such as window systems.sup.2, text editors.sup.3 and drawing tools.sup.4 allow users at different workstations to make changes simultaneously. These systems permit some types of local user preferences.sup.5. One simple system of this type is Commune.sup.4 which allows users to simultaneously draw with a stylus on the pages of a shared electronic notebook. This latter system shows the same image to all users and uses colored cursors and objects to distinguish among different users.
SharedArk.sup.6 supports collaborative learning of physics by allowing users to simulate experiments. In this system, users move around a planar space that contains objects that they can manipulate. When users' view of the plane overlap, the views are WYSIWIS in the shared region. Each user controls a pointer, labeled with the user's name, that is visible on all conference screens. Any user can manipulate any object in his or her view. Buttons in this system can be applied to any object, and shared between users. This system also supports per-user pointers, shared buttons and objects, lightweight locking of objects, and equal status of participants.
Several systems support meetings by allowing participants, working at individual workstations, to control a large shared screen. Some use chalk-passing floor control, such as the Capture Lab.sup.7 Others allow simultaneous editing, such as Colab.sup.8. The Colab team, in reporting on the Cognoter tool, noted that simultaneous access to the screen improves brainstorming because users need not wait for others to complete an entry before making their own contribution. They also noted that shared user interfaces need to be simple, because there is little time for training in a group setting. In all of these systems, however, the number of active participants is limited by the number of machines and the participants must go to a special meeting room.